This invention generally relates to a high pressure damage resistant decorative laminate having excellent scratch, mar, scrape and abrasion resistance, as well as excellent appearance and cleanability and methods of producing the same. More particularly, this invention relates to damage resistant, decorative laminates employing a decorative sheet saturated with a melamine-formaldehyde resin coating incorporating abrasive materials.
Conventionally, high pressure decorative laminates are made of two essential layers: a core layer and a surface layer. The core layer constitutes a bottom or supporting layer onto which the other layer is bonded. In normal high-pressure laminate manufacture, the core layer consists of a plurality of cellulosic sheets. The core sheets are generally made from a kraft paper impregnated with a laminating resin. Laminating resins commonly used for the core layer include phenolic, amino, epoxy, polyester, silicone, and diallyl phthalate resins to name a few. The industrially preferred laminating resin for decorative laminates is a phenolic resin made from the reaction of phenols with formaldehyde.
Placed above the core layer is a decorative layer which is generally an alpha cellulose pigmented paper containing a print, pattern design or solid color that has been impregnated with a melamine-formaldehyde resin.
The cured melamine-formaldehyde resins are colorless and resistant to light; they are resistant to a variety of solvents and stains; and their heat resistance make them resistant to burning cigarettes, boiling water and heated containers up to about 325.degree. F. Without these melamine-formaldehyde resins, the decorative laminate industry would not exist as it is known today. However, because these resins are extremely brittle, they sometimes require reinforcement.
When the decorative layer of the laminate is a printed pattern, it is covered with an overlay as it is commonly referred to, which is a high-quality alpha cellulose paper impregnated with a melamine-formaldehyde resin. This layer protects the decorative print from external abuse such as abrasive wear and tear, harsh chemicals, burns, spills and the like. It is primarily the melamine-formaldehyde resin which accounts for these protective properties of the laminate. The alpha-cellulose paper acts as a translucent carrier for the water-thin resin, imparts strength to the rather brittle melamine-formaldehyde resin, maintains a uniform resin thickness in the overlay by acting as a shim, and controls resin flow.
The core layer, decorative layer and the overlay surface layer (when needed) are stacked in a superimposed relationship, between steel press plates and subjected to a pressure and temperature for a time sufficiently long enough to cure the laminating resins impregnating the respective layers. The elevated temperature and pressure actually cause the impregnated resins within the sheets to flow, which consolidates the whole into an integral mass known as the laminate. These laminates are used as surfacings for counter tops, table tops, furniture, store fixtures and the like. However, these conventional high pressure laminates can be easily damaged by scraping or marring caused by objects sliding across the surface of the laminate.
Abrasive materials have previously been employed in the overlay sheet or solid color decorative sheet in order to improve the abrasion resistance of these high pressure decorative laminates. The abrasive materials are generally deposited upon the alpha cellulose matrix or, in other applications, mixed with a binder such as cellulosic fibers or microcrystalline materials replacing the alpha cellulose overlay sheet. Damage resistant high pressure decorative laminates incorporating abrasive materials are well known. However, these damage resistant decorative laminates have required the presence of a binder material preferably microcrystalline cellulose in order to bind the abrasive materials to the overlay or decorative sheet. Also, these damage resistant high pressure decorating laminates have been produced by difficult and expensive multi-step processes which requires that the abrasive material and binder be added in a separate step from the resin material and requiring that the decorative sheet be first coated with the abrasive materials and the binder material and then dried to bind the abrasive materials to the decorative sheet. The decorative sheet would then be impregnated with a thermosetting resin. Additionally, those damage resistant laminates which have the most durable surfaces generally have dull, non-uniform, unattractive surfaces that feel rough, grab and hold dirt, and are difficult to clean.
Thus, there exists a need for a damage resistant decorative laminate which has excellent scratch, mar and scrape resistance and which does not need to employ the use of a binder material to bind the abrasion resistant particles to the decorative sheet. Additionally, there exists a need for a damage resistant decorative laminate that can be produced without the costly multi-step process which requires separate coating and drying steps to adhere the abrasion resistant particles and binder material and impregnating steps to apply the resin. Further, there exists a need for a damage resistant laminate which has a very uniform appearance, an attractive sheen, a smooth feel and easy cleanability.